DiCaprio stars in the Clint Eastwood-directed film as the late FBI boss J. Edgar Hoover. DiCaprio's portrayal spans several decades, beginning with Hoover in his 20s through around the time of his death in 1972 at age 77.

Makeup and prosthetics used for the later years left DiCaprio practically unrecognizable.

"I was on the set my first day and I look over and there's someone getting sound and I was like, 'I don't know who the old guy is, but where's Leo?'" Eric Matheny, who plays Hoover's doctor in the movie, told me at the L.A. premiere of The Tree of Life. "But then I looked over again and it was like, 'That's Leo?!' I could see it was him in his eyes, but everything else was completely different."

It certainly didn't come easy. "He was buried in makeup," Matheny said. "He was six hours in makeup for almost 12-hour days. His endurance was astounding."

As for Matheny's role, the character he portrays is a doctor who makes daily visits to Hoover's office. "It sounds like he had someone shooting him up with something because you don't need a doctor to come to you on a daily basis to give you pills and a glass of water," Matheny said of the character. "Basically, I'm Dr. Feelgood...As Hoover gets older he gets, as Clint Eastwood says, 'a B12 shot with a little something extra.'"